Logic Outputs Problem in 7493 IC

I will answer soon but not today.

Hello,
Very interesting observation that you made with the current through the 7493 !!!!
"The Q outputs of the 74LS93 can only source -800 uA (Ioh) whereas they can sink 16mA (Iol) See page six at this link."
I couldnt see it myself, without your help, not in a million years. Yah, very good catch there. Respect for that !
- - -
I've --simulated-- YOUR (private) suggestion with the PNPs. And I made it work !
Of course from the 100th time, but it did.
I had to include those NOT gates to normalize the output from the PNP's. Also I had to tweak some resistors values as well, to make it work at full capacity. 10k on the Base of the tr's was too much and the voltage was too small on those bus wires. I made them 3k and I got 5V per PNP output, on each colector.
Sourcing and sinking the current through the transistors... Very interesting tweak !
Now Im very curious how it will actually work in reality. The simulator is giving (sometimes) false positives. I'll update you soon.
Thanks so far !

f

Seems we make a good partnership.

marconi said:

Seems we make a good partnership.

Click to expand...

Yes....heh....dont say 'hop' yet.
---in reality--- it didnt work. I told you, I get false positives from the simulator.
Is a bit of explanation of what I did.
I used c556b for the PNPs. I have them brand new from 2000's. Rarely used, once or twice.
For the NOT gate, I used 74LS04

I got 150mA through the entire cct (read from the PSU) because I used the 100R on the gnd. And I change them to 300R and I get 80mA through the entire cct. Without them in the cct, I get 10mA. The 100R were getting very hot as well, while the 300R not so much.
I marked as -Ds1- and -Ds2- the 2 sets of Diodes I used on my breadboard. I didnt build ALL of this, only parts to see if its working.


What all this means?
Ds1 are set to count to a fixed number. Ok? In this case I set it to count to 8 for testing purposes.
Ds2 are set to --display-- number #1. It's their only job. When counter pass through #1 from its counting program(to 8), this part will display #1 is activated. Very simple.
I hope it is very clear now.
The problems:
- #1 LED is not lighting at all ! It should, as in the simulator.
I probe with osc the base of the tr next to #1 and no visible signal.
I probe the 300R, all of them , and no visible signal.
I probe the base of all 4 PNP tr's , and no visible signal.
I only get a ~3Vish(or so) signal on the NOT output to the base of the first PNP. No signal on the input of the NOT gate.
And the probes of the osciloscope I had to inverse them. I connected the (+) probe to the (+)rail of 5V. And the (-) probe on the output and I could get a reading - only this way !


I got a very-very-VERY low reading, almost imperceptible on the #1 diode in Ds2 group. And only when using the 300R !!! When I used 100R, nothing. Very perplexing ! Also with the osc probes inverted (probing with the (-) on the pins there, to actually see a reading !!! ).


Ive also did an experiment. Initially I put a white LED on #1. And I thought, well, maybe is not sensitive enough (and I was very right) and I change it to a red LED as you can see in the picture. I get crazy sometimes and try everything. You know. And from my MANY permutations I did, I reach this stage when I eliminated some 300R and some diodes in Ds2. The effect was interesting to mention to you. The LED was LIT but like 50% lit. Ok? But it was pulsating. It was getting even more lit, to 75% LIT. Ok? And back to 50 and back to 75 and so on. So it is a signal on the line !!!!! Thats my observation.
The VERY small imperceptible signal confirmed this LED LIT exception experimentation.

Thats it.

I will take a closer look over the next few days.

Are the LEDs in an array with their cathodes all connected together like this:



Or are the LEDs all separate and you have connected their cathodes together and then to 0V?

For circuit around #1 transistor the diode connected to the left of R199 is incorrect. Have you done the same for the transistor circuit below numbered #2?

How are the 16 LEDs to be lit? One LED of 16 or n of 16 where n is the count state?

eg for count state n=3 where count starts at state 0 and goes up state 15:

off off off on off off..off

or

on on on on off off off….off

Here is the full cct. Zoom in it to see the details. Its a big file.

or here where you can really see it in original resolution https://www.deviantart.com/q12a/art/CountingOutputLEDs-v1A-944060484
also you can download the image and inspect it in your favorite image viewer in your windows.
Hmmm.... I am using some custom LEDs in my drawing and you cant see the direction they are pointing. They are towards GND. All of them.

Hold on I actually show their direction ...I guess was not that clear to others...it was very clear to me. You see that green bar next to the led? Like a diode that has a line designating the (-) side. I really thought is intuitive enough. Hmmm. is not looking like a conventional LED, that is very true....

marconi said:

How are the 16 LEDs to be lit? One LED of 16 or n of 16 where n is the count state?

Click to expand...

Ive also shown this part as well. In #1 post I made here in this thread. Look with attention on the picture there and you will see a single green light glow. Ive also explain it in words what it does. You should re-read my #1 post.
I will prepare a video and showing that is indeed working but only here in simulator. Not in reality. Hold on.

marconi said:

Are the LEDs in an array with their cathodes all connected together like this

View attachment 105082

Or are the LEDs all separate and you have connected their cathodes together and then to 0V?

Click to expand...

Answering my own question by studying your bread board in #5, you are using discrete red LEDs, each of which has their cathode connected to 0V and their anode to +5V via a 1kR resistor. You turn them on and off by a transistor in parallel with the LED, a way I find unusual.

Now I have been able to study your DS and # circuitry, you have built your own version of diode transistor logic (DTL)gates and by connecting its inputs appropriately to the four busbars for QA, QB, QC and QD you can use these gates to carry out a 4-term logic operation appropriate to selecting one of the 16 LEDs to illuminate eg D* . C* . B . A to light the fourth LED when the 93 counter is in binary state 0011 or count n = 3; n is in the range 0 to 15.

These logic scheme will light only one LED at a time, 0 to 15 and then repeating.

I reckon that only one of your DTL gates connected to the logic busbars will probably work fine. The problem arises when you have more than one because they interact with each via the logic busbars. This is because they are current driven not purely voltage driven. Let me pause there on my critique of your circuit.

It appears to me that your project aim is to construct combinational logic to convert a 4 bit binary code into a one of 16 code. You could do this using logic ics which you could buy - NANDs being typical because you can make all logic functions using these. You have decided not to. Instead you are enjoying building from scratch your own logic gates using DTL technology.

https://www.niser.ac.in/sps/sites/default/files/basic_page/logic gate circuits.pdf

I suggest you study the section in this tutorial on DTL. And furthermore that you switch the current to an LED rather than divert the current away from the LED. And, that you connect the 16 LEDs anodes to +5V and use a transistor to sink each to 0V.

Aim to make a DTL NAND and a DTL Inverter because with these you can do any logic operation.

PS: (In my projects I use a NAND or an inverter gates to sink an LED to 0V via a 1kR resistor. A logic 1 at their inputs turns on the LED which is an example of positive logic - if something is true then something else is true.)

Did you watched my movie?

marconi said:

Instead you are enjoying building from scratch your own logic gates using DTL technology.

Click to expand...

Im not enjoying anything. Im only finding the best intuitive ways I can make this work.
My aim is to get 4 wires (the bus wires) and output from them every combination. Up to 16. But is impossible to make it with only 1 one BCD. I tried 3 of them and I failed on cascading them. I can use 1 single BCD and the rest, from 9 to 16 using this DTL way.
Then I thought, for testing purposes I will use everything made of DTL starting from 0. And thats the history I reach this stage.
Hope is clear enough now. Watch my movie and you can skip through it. Im explaining there a lot of details.
Thanks.